1. Field of the Invention
The present invention relates to an apparatus and method for correcting the edge of an image, and more particularly, to an apparatus and method for correcting the sharpness of the edge of an image. The present application is based on Korean Patent Application No. 2001-82482, which is incorporated herein by reference.
2. Description of the Related Art
In general, the quality of an image is determined by the sharpness of the edge of the image. Thus, techniques for correcting the sharpness of the edge of an image have been developed.
FIG. 1 is a block diagram of a conventional apparatus for correcting the edge of an image. Referring to FIG. 1, when an image signal is input to a first differentiator 101, the first differentiator 101 differentiates the image signal and measures the intensity and direction of the edge of the image signal. Then, a second differentiator 102 differentiates the image signal from the first differentiator 101 and extracts the edge of the image signal. The second differentiator 102 measures only the intensity of the edge of the image signal. The edge of the image extracted in the second differentiator 102 forms a closed curve. The extracted edge of the image is transmitted to a multiplier 103. Then, the multiplier 103 multiplies the edge of the image by a predetermined gain so that the sharpness of the extracted edge can be corrected. The edge data from the multiplier 103 is transmitted to a coring 104.
The coring 104 blocks the amplification of noise present in the low frequency band. Accordingly, the coring 104 compares the edge data transmitted from the multiplier 103 with a predetermined value and converts the edge data, which has a lower frequency band than the predetermined value, into 0. The converted edge data is transmitted to an adder 105.
Next, the adder 105 adds the edge data image from the coring 104 and the input image signal and then transmits the result to a clipping circuit 106. The clipping circuit 106 clips the image signal from the adder 105 so that its luminance level falls within a range of 0–255. The clipped image signal is output as an image signal whose edge is improved.
However, the second differentiator 102 is not sensitive to an image signal whose brightness changes gradually. Thus, it is difficult to detect the edge of an image whose brightness gradually changes using the apparatus of FIG. 1. Further, the apparatus of FIG. 1 is set such that the extracted edge data of an image is multiplied by a fixed gain using the first and second differentiators 101 and 102, irrespective of the brightness level of the edge. Thus, there is a possibility of overshoot or undershoot occurring at the edge of an image when the edge of an image signal is to be corrected using the apparatus of FIG. 1.